I want to make it so when I hit the key followed by another letter, such as 'a', 'e', or 'u', it adds it as a grave. I know this is possible, 'cause if you put your keyboard layout in German, and hit the '+' (on american keyboards) key and follow it with 'a', 'e', 'i', etc., it will add it for example ('+' (on a German layout is '') + ‘a’) = ’
Please see the Frequently Asked Questions in the support forum.
Your problem is not related to creating fonts, it has to do with keyboard input. I suggest you download the free Microsoft Keyboard Layout Creator. In that application you can program the ` key (or any key, for that matter) as a dead key.